* Revised fmemopen(3) man page
@ 2016-03-09 4:19 Michael Kerrisk (man-pages)
[not found] ` <56DFA46F.1050509-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
0 siblings, 1 reply; 3+ messages in thread
From: Michael Kerrisk (man-pages) @ 2016-03-09 4:19 UTC (permalink / raw)
To: Adhemerval Zanella, Paul Pluzhnikov
Cc: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w, linux-man, libc-alpha
Hello Adhemerval
Since you recently did a reimplementation of fmemopen() (which
Paul reminded me of) I've similarly just now done a major rework
of the man page. Might you (or Paul, feel free to also chin in!),
be willing to take a look at the text below and let me know if
anything needs fixing?
Thanks,
Michael
NAME
fmemopen - open memory as stream
SYNOPSIS
#include <stdio.h>
FILE *fmemopen(void *buf, size_t size, const char *mode);
Feature Test Macro Requirements for glibc (see fea‐
ture_test_macros(7)):
fmemopen():
Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_GNU_SOURCE
DESCRIPTION
The fmemopen() function opens a stream that permits the access
specified by mode. The stream allows I/O to be performed on
the string or memory buffer pointed to by buf.
The mode argument specifies the semantics of I/O on the stream,
and is one of the following:
r The stream is opened for reading.
w The stream is opened for writing.
a Append; open the stream for writing, with the file ini‐
tial position set to the first null byte.
r+ Open the stream for reading and writing.
w+ Open the stream for reading and writing. The buffer
contents are truncated (i.e., '\0' is placed in the
first byte of the buffer).
a+ Append; open the stream for reading and writing, with
the file initial position set to the first null byte.
The stream maintains the notion of a current position, the
location where the next I/O operation will be performed. The
current position is implicitly updated by I/O operations. It
can be explicitly updated using fseek(3), and determined using
ftell(3). In all modes other than append, the initial position
is set to the start of the buffer. In append mode, if no null
byte is found within the buffer, then the initial position is
size+1.
If buf is specified as NULL, then fmemopen() allocates a buffer
of size bytes. This is useful for an application that wants to
write data to a temporary buffer and then read it back again.
The initial position is set to the start of the buffer. The
buffer is automatically freed when the stream is closed. Note
that the caller has no way to obtain a pointer to the temporary
buffer allocated by this call (but see open_memstream(3)).
If buf is not NULL, then it should point to a buffer of at
least len bytes allocated by the caller.
When a stream that has been opened for writing is flushed
(fflush(3)) or closed (fclose(3)), a null byte is written at
the end of the buffer if there is space. The caller should
ensure that an extra byte is available in the buffer (and that
size counts that byte) to allow for this.
In a stream opened for reading, null bytes ('\0') in the buffer
do not cause read operations to return an end-of-file indica‐
tion. A read from the buffer will indicate end-of-file only
when the file current position advances size bytes past the
start of the buffer.
Write operations take place either at the current position (for
modes other than append), or at the current size of the stream
(for append modes).
Attempts to write more than size bytes to the buffer result in
an error. By default, such errors will be visible (by the
absence of data) only when the stdio buffer is flushed. Dis‐
abling buffering with the following call may be useful to
detect errors at the time of an output operation:
setbuf(stream, NULL);
Alternatively, the caller can explicitly set buf as the stdio
stream buffer, at the same time informing stdio of the buffer's
size, using:
setbuffer(stream, buf, size);
RETURN VALUE
Upon successful completion, fmemopen() returns a FILE pointer.
Otherwise, NULL is returned and errno is set to indicate the
error.
VERSIONS
fmemopen() was already available in glibc 1.0.x.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
┌────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────┼───────────────┼─────────┤
│fmemopen(), │ Thread safety │ MT-Safe │
└────────────┴───────────────┴─────────┘
CONFORMING TO
POSIX.1-2008. This function is not specified in POSIX.1-2001,
and is not widely available on other systems.
POSIX.1-2008 specifies that 'b' in mode shall be ignored. How‐
ever, Technical Corrigendum 1 adjusts the standard to allow
implementation-specific treatment for this case, thus permit‐
ting the glibc treatment of 'b'.
NOTES
There is no file descriptor associated with the file stream
returned by this function (i.e., fileno(3) will return an error
if called on the returned stream).
With version 2.22, binary mode (see below) was removed, many
longstanding bugs in the implementation of fmemopen() were
fixed, and a new versioned symbol was created for this inter‐
face.
Binary mode
From version 2.9 to 2.21, the glibc implementation of fmemo‐
pen() supported a "binary" mode, enabled by specifying the let‐
ter 'b' as the second character in mode. In this mode, writes
don't implicitly add a terminating null byte, and fseek(3)
SEEK_END is relative to the end of the buffer (i.e., the value
specified by the size argument), rather than the current string
length.
An API bug afflicted the implementation of binary mode: to
specify binary mode, the 'b' must be the second character in
mode. Thus, for example, "wb+" has the desired effect, but
"w+b" does not. This is inconsistent with the treatment of
mode by fopen(3).
Binary mode was removed in glibc 2.22; a 'b' specified in mode
has no effect.
BUGS
In versions of glibc before 2.22, if size is specified as zero,
fmemopen() fails with the error EINVAL. It would be more con‐
sistent if this case successfully created a stream that then
returned end of file on the first attempt at reading; since
version 2.22, the glibc implementation provides that behavior.
In versions of glibc before 2.22, specifying append mode ("a"
or "a+") for fmemopen() sets the initial buffer position to the
first null byte, but (if the file offset is reset to a location
other than the end of the stream) does not force subsequent
writes to append at the end of the stream. This bug is fixed
in glibc 2.22.
In versions of glibc before 2.22, if the mode argument to fmem‐
open() specifies append ("a" or "a+"), and the size argument
does not cover a null byte in buf, then, according to
POSIX.1-2008, the initial buffer position should be set to the
next byte after the end of the buffer. However, in this case
the glibc fmemopen() sets the buffer position to -1. This bug
is fixed in glibc 2.22.
In versions of glibc before 2.22, when a call to fseek(3) with
a whence value of SEEK_END was performed on a stream created by
fmemopen(), the offset was subtracted from the end-of-stream
position, instead of being added. This bug is fixed in glibc
2.22.
The glibc 2.9 addition of "binary" mode for fmemopen() silently
changed the ABI: previously, fmemopen() ignored 'b' in mode.
EXAMPLE
The program below uses fmemopen() to open an input buffer, and
open_memstream(3) to open a dynamically sized output buffer.
The program scans its input string (taken from the program's
first command-line argument) reading integers, and writes the
squares of these integers to the output buffer. An example of
the output produced by this program is the following:
$ ./a.out '1 23 43'
size=11; ptr=1 529 1849
Program source
#define _GNU_SOURCE
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define handle_error(msg) \
do { perror(msg); exit(EXIT_FAILURE); } while (0)
int
main(int argc, char *argv[])
{
FILE *out, *in;
int v, s;
size_t size;
char *ptr;
if (argc != 2) {
fprintf(stderr, "Usage: %s '<num>...'\n", argv[0]);
exit(EXIT_FAILURE);
}
in = fmemopen(argv[1], strlen(argv[1]), "r");
if (in == NULL)
handle_error("fmemopen");
out = open_memstream(&ptr, &size);
if (out == NULL)
handle_error("open_memstream");
for (;;) {
s = fscanf(in, "%d", &v);
if (s <= 0)
break;
s = fprintf(out, "%d ", v * v);
if (s == -1)
handle_error("fprintf");
}
fclose(in);
fclose(out);
printf("size=%zu; ptr=%s\n", size, ptr);
free(ptr);
exit(EXIT_SUCCESS);
}
SEE ALSO
fopen(3), fopencookie(3), open_memstream(3)
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
--
To unsubscribe from this list: send the line "unsubscribe linux-man" in
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Revised fmemopen(3) man page
[not found] ` <56DFA46F.1050509-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
@ 2016-03-11 4:15 ` Adhemerval Zanella
2016-03-11 16:33 ` Michael Kerrisk (man-pages)
0 siblings, 1 reply; 3+ messages in thread
From: Adhemerval Zanella @ 2016-03-11 4:15 UTC (permalink / raw)
To: Michael Kerrisk (man-pages), Paul Pluzhnikov; +Cc: linux-man, libc-alpha
I am not the most qualified person to correct syntactic issues or
grammar, but regarding the contents it covers current functionalities
and previous bugs as I would expect, thanks!
On 09-03-2016 11:19, Michael Kerrisk (man-pages) wrote:
> Hello Adhemerval
>
> Since you recently did a reimplementation of fmemopen() (which
> Paul reminded me of) I've similarly just now done a major rework
> of the man page. Might you (or Paul, feel free to also chin in!),
> be willing to take a look at the text below and let me know if
> anything needs fixing?
>
> Thanks,
>
> Michael
>
> NAME
> fmemopen - open memory as stream
>
> SYNOPSIS
> #include <stdio.h>
>
> FILE *fmemopen(void *buf, size_t size, const char *mode);
>
> Feature Test Macro Requirements for glibc (see fea‐
> ture_test_macros(7)):
>
> fmemopen():
> Since glibc 2.10:
> _POSIX_C_SOURCE >= 200809L
> Before glibc 2.10:
> _GNU_SOURCE
>
> DESCRIPTION
> The fmemopen() function opens a stream that permits the access
> specified by mode. The stream allows I/O to be performed on
> the string or memory buffer pointed to by buf.
>
> The mode argument specifies the semantics of I/O on the stream,
> and is one of the following:
>
> r The stream is opened for reading.
>
> w The stream is opened for writing.
>
> a Append; open the stream for writing, with the file ini‐
> tial position set to the first null byte.
>
> r+ Open the stream for reading and writing.
>
> w+ Open the stream for reading and writing. The buffer
> contents are truncated (i.e., '\0' is placed in the
> first byte of the buffer).
>
> a+ Append; open the stream for reading and writing, with
> the file initial position set to the first null byte.
>
> The stream maintains the notion of a current position, the
> location where the next I/O operation will be performed. The
> current position is implicitly updated by I/O operations. It
> can be explicitly updated using fseek(3), and determined using
> ftell(3). In all modes other than append, the initial position
> is set to the start of the buffer. In append mode, if no null
> byte is found within the buffer, then the initial position is
> size+1.
>
> If buf is specified as NULL, then fmemopen() allocates a buffer
> of size bytes. This is useful for an application that wants to
> write data to a temporary buffer and then read it back again.
> The initial position is set to the start of the buffer. The
> buffer is automatically freed when the stream is closed. Note
> that the caller has no way to obtain a pointer to the temporary
> buffer allocated by this call (but see open_memstream(3)).
>
> If buf is not NULL, then it should point to a buffer of at
> least len bytes allocated by the caller.
>
> When a stream that has been opened for writing is flushed
> (fflush(3)) or closed (fclose(3)), a null byte is written at
> the end of the buffer if there is space. The caller should
> ensure that an extra byte is available in the buffer (and that
> size counts that byte) to allow for this.
>
> In a stream opened for reading, null bytes ('\0') in the buffer
> do not cause read operations to return an end-of-file indica‐
> tion. A read from the buffer will indicate end-of-file only
> when the file current position advances size bytes past the
> start of the buffer.
>
> Write operations take place either at the current position (for
> modes other than append), or at the current size of the stream
> (for append modes).
>
> Attempts to write more than size bytes to the buffer result in
> an error. By default, such errors will be visible (by the
> absence of data) only when the stdio buffer is flushed. Dis‐
> abling buffering with the following call may be useful to
> detect errors at the time of an output operation:
>
> setbuf(stream, NULL);
>
> Alternatively, the caller can explicitly set buf as the stdio
> stream buffer, at the same time informing stdio of the buffer's
> size, using:
>
> setbuffer(stream, buf, size);
>
> RETURN VALUE
> Upon successful completion, fmemopen() returns a FILE pointer.
> Otherwise, NULL is returned and errno is set to indicate the
> error.
>
> VERSIONS
> fmemopen() was already available in glibc 1.0.x.
>
> ATTRIBUTES
> For an explanation of the terms used in this section, see
> attributes(7).
>
> ┌────────────┬───────────────┬─────────┐
> │Interface │ Attribute │ Value │
> ├────────────┼───────────────┼─────────┤
> │fmemopen(), │ Thread safety │ MT-Safe │
> └────────────┴───────────────┴─────────┘
>
> CONFORMING TO
> POSIX.1-2008. This function is not specified in POSIX.1-2001,
> and is not widely available on other systems.
>
> POSIX.1-2008 specifies that 'b' in mode shall be ignored. How‐
> ever, Technical Corrigendum 1 adjusts the standard to allow
> implementation-specific treatment for this case, thus permit‐
> ting the glibc treatment of 'b'.
>
> NOTES
> There is no file descriptor associated with the file stream
> returned by this function (i.e., fileno(3) will return an error
> if called on the returned stream).
>
> With version 2.22, binary mode (see below) was removed, many
> longstanding bugs in the implementation of fmemopen() were
> fixed, and a new versioned symbol was created for this inter‐
> face.
>
> Binary mode
> From version 2.9 to 2.21, the glibc implementation of fmemo‐
> pen() supported a "binary" mode, enabled by specifying the let‐
> ter 'b' as the second character in mode. In this mode, writes
> don't implicitly add a terminating null byte, and fseek(3)
> SEEK_END is relative to the end of the buffer (i.e., the value
> specified by the size argument), rather than the current string
> length.
>
> An API bug afflicted the implementation of binary mode: to
> specify binary mode, the 'b' must be the second character in
> mode. Thus, for example, "wb+" has the desired effect, but
> "w+b" does not. This is inconsistent with the treatment of
> mode by fopen(3).
>
> Binary mode was removed in glibc 2.22; a 'b' specified in mode
> has no effect.
>
> BUGS
> In versions of glibc before 2.22, if size is specified as zero,
> fmemopen() fails with the error EINVAL. It would be more con‐
> sistent if this case successfully created a stream that then
> returned end of file on the first attempt at reading; since
> version 2.22, the glibc implementation provides that behavior.
>
> In versions of glibc before 2.22, specifying append mode ("a"
> or "a+") for fmemopen() sets the initial buffer position to the
> first null byte, but (if the file offset is reset to a location
> other than the end of the stream) does not force subsequent
> writes to append at the end of the stream. This bug is fixed
> in glibc 2.22.
>
> In versions of glibc before 2.22, if the mode argument to fmem‐
> open() specifies append ("a" or "a+"), and the size argument
> does not cover a null byte in buf, then, according to
> POSIX.1-2008, the initial buffer position should be set to the
> next byte after the end of the buffer. However, in this case
> the glibc fmemopen() sets the buffer position to -1. This bug
> is fixed in glibc 2.22.
>
> In versions of glibc before 2.22, when a call to fseek(3) with
> a whence value of SEEK_END was performed on a stream created by
> fmemopen(), the offset was subtracted from the end-of-stream
> position, instead of being added. This bug is fixed in glibc
> 2.22.
>
> The glibc 2.9 addition of "binary" mode for fmemopen() silently
> changed the ABI: previously, fmemopen() ignored 'b' in mode.
>
> EXAMPLE
> The program below uses fmemopen() to open an input buffer, and
> open_memstream(3) to open a dynamically sized output buffer.
> The program scans its input string (taken from the program's
> first command-line argument) reading integers, and writes the
> squares of these integers to the output buffer. An example of
> the output produced by this program is the following:
>
> $ ./a.out '1 23 43'
> size=11; ptr=1 529 1849
>
> Program source
>
> #define _GNU_SOURCE
> #include <string.h>
> #include <stdio.h>
> #include <stdlib.h>
>
> #define handle_error(msg) \
> do { perror(msg); exit(EXIT_FAILURE); } while (0)
>
> int
> main(int argc, char *argv[])
> {
> FILE *out, *in;
> int v, s;
> size_t size;
> char *ptr;
>
> if (argc != 2) {
> fprintf(stderr, "Usage: %s '<num>...'\n", argv[0]);
> exit(EXIT_FAILURE);
> }
>
> in = fmemopen(argv[1], strlen(argv[1]), "r");
> if (in == NULL)
> handle_error("fmemopen");
>
> out = open_memstream(&ptr, &size);
> if (out == NULL)
> handle_error("open_memstream");
>
> for (;;) {
> s = fscanf(in, "%d", &v);
> if (s <= 0)
> break;
>
> s = fprintf(out, "%d ", v * v);
> if (s == -1)
> handle_error("fprintf");
> }
>
> fclose(in);
> fclose(out);
>
> printf("size=%zu; ptr=%s\n", size, ptr);
>
> free(ptr);
> exit(EXIT_SUCCESS);
> }
>
> SEE ALSO
> fopen(3), fopencookie(3), open_memstream(3)
>
>
--
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Revised fmemopen(3) man page
2016-03-11 4:15 ` Adhemerval Zanella
@ 2016-03-11 16:33 ` Michael Kerrisk (man-pages)
0 siblings, 0 replies; 3+ messages in thread
From: Michael Kerrisk (man-pages) @ 2016-03-11 16:33 UTC (permalink / raw)
To: Adhemerval Zanella, Paul Pluzhnikov; +Cc: mtk.manpages, linux-man, libc-alpha
On 03/11/2016 05:15 AM, Adhemerval Zanella wrote:
> I am not the most qualified person to correct syntactic issues or
> grammar, but regarding the contents it covers current functionalities
> and previous bugs as I would expect, thanks!
Thanks for checking the page over, Adhemerval!
Cheers,
Michael
> On 09-03-2016 11:19, Michael Kerrisk (man-pages) wrote:
>> Hello Adhemerval
>>
>> Since you recently did a reimplementation of fmemopen() (which
>> Paul reminded me of) I've similarly just now done a major rework
>> of the man page. Might you (or Paul, feel free to also chin in!),
>> be willing to take a look at the text below and let me know if
>> anything needs fixing?
>>
>> Thanks,
>>
>> Michael
>>
>> NAME
>> fmemopen - open memory as stream
>>
>> SYNOPSIS
>> #include <stdio.h>
>>
>> FILE *fmemopen(void *buf, size_t size, const char *mode);
>>
>> Feature Test Macro Requirements for glibc (see fea‐
>> ture_test_macros(7)):
>>
>> fmemopen():
>> Since glibc 2.10:
>> _POSIX_C_SOURCE >= 200809L
>> Before glibc 2.10:
>> _GNU_SOURCE
>>
>> DESCRIPTION
>> The fmemopen() function opens a stream that permits the access
>> specified by mode. The stream allows I/O to be performed on
>> the string or memory buffer pointed to by buf.
>>
>> The mode argument specifies the semantics of I/O on the stream,
>> and is one of the following:
>>
>> r The stream is opened for reading.
>>
>> w The stream is opened for writing.
>>
>> a Append; open the stream for writing, with the file ini‐
>> tial position set to the first null byte.
>>
>> r+ Open the stream for reading and writing.
>>
>> w+ Open the stream for reading and writing. The buffer
>> contents are truncated (i.e., '\0' is placed in the
>> first byte of the buffer).
>>
>> a+ Append; open the stream for reading and writing, with
>> the file initial position set to the first null byte.
>>
>> The stream maintains the notion of a current position, the
>> location where the next I/O operation will be performed. The
>> current position is implicitly updated by I/O operations. It
>> can be explicitly updated using fseek(3), and determined using
>> ftell(3). In all modes other than append, the initial position
>> is set to the start of the buffer. In append mode, if no null
>> byte is found within the buffer, then the initial position is
>> size+1.
>>
>> If buf is specified as NULL, then fmemopen() allocates a buffer
>> of size bytes. This is useful for an application that wants to
>> write data to a temporary buffer and then read it back again.
>> The initial position is set to the start of the buffer. The
>> buffer is automatically freed when the stream is closed. Note
>> that the caller has no way to obtain a pointer to the temporary
>> buffer allocated by this call (but see open_memstream(3)).
>>
>> If buf is not NULL, then it should point to a buffer of at
>> least len bytes allocated by the caller.
>>
>> When a stream that has been opened for writing is flushed
>> (fflush(3)) or closed (fclose(3)), a null byte is written at
>> the end of the buffer if there is space. The caller should
>> ensure that an extra byte is available in the buffer (and that
>> size counts that byte) to allow for this.
>>
>> In a stream opened for reading, null bytes ('\0') in the buffer
>> do not cause read operations to return an end-of-file indica‐
>> tion. A read from the buffer will indicate end-of-file only
>> when the file current position advances size bytes past the
>> start of the buffer.
>>
>> Write operations take place either at the current position (for
>> modes other than append), or at the current size of the stream
>> (for append modes).
>>
>> Attempts to write more than size bytes to the buffer result in
>> an error. By default, such errors will be visible (by the
>> absence of data) only when the stdio buffer is flushed. Dis‐
>> abling buffering with the following call may be useful to
>> detect errors at the time of an output operation:
>>
>> setbuf(stream, NULL);
>>
>> Alternatively, the caller can explicitly set buf as the stdio
>> stream buffer, at the same time informing stdio of the buffer's
>> size, using:
>>
>> setbuffer(stream, buf, size);
>>
>> RETURN VALUE
>> Upon successful completion, fmemopen() returns a FILE pointer.
>> Otherwise, NULL is returned and errno is set to indicate the
>> error.
>>
>> VERSIONS
>> fmemopen() was already available in glibc 1.0.x.
>>
>> ATTRIBUTES
>> For an explanation of the terms used in this section, see
>> attributes(7).
>>
>> ┌────────────┬───────────────┬─────────┐
>> │Interface │ Attribute │ Value │
>> ├────────────┼───────────────┼─────────┤
>> │fmemopen(), │ Thread safety │ MT-Safe │
>> └────────────┴───────────────┴─────────┘
>>
>> CONFORMING TO
>> POSIX.1-2008. This function is not specified in POSIX.1-2001,
>> and is not widely available on other systems.
>>
>> POSIX.1-2008 specifies that 'b' in mode shall be ignored. How‐
>> ever, Technical Corrigendum 1 adjusts the standard to allow
>> implementation-specific treatment for this case, thus permit‐
>> ting the glibc treatment of 'b'.
>>
>> NOTES
>> There is no file descriptor associated with the file stream
>> returned by this function (i.e., fileno(3) will return an error
>> if called on the returned stream).
>>
>> With version 2.22, binary mode (see below) was removed, many
>> longstanding bugs in the implementation of fmemopen() were
>> fixed, and a new versioned symbol was created for this inter‐
>> face.
>>
>> Binary mode
>> From version 2.9 to 2.21, the glibc implementation of fmemo‐
>> pen() supported a "binary" mode, enabled by specifying the let‐
>> ter 'b' as the second character in mode. In this mode, writes
>> don't implicitly add a terminating null byte, and fseek(3)
>> SEEK_END is relative to the end of the buffer (i.e., the value
>> specified by the size argument), rather than the current string
>> length.
>>
>> An API bug afflicted the implementation of binary mode: to
>> specify binary mode, the 'b' must be the second character in
>> mode. Thus, for example, "wb+" has the desired effect, but
>> "w+b" does not. This is inconsistent with the treatment of
>> mode by fopen(3).
>>
>> Binary mode was removed in glibc 2.22; a 'b' specified in mode
>> has no effect.
>>
>> BUGS
>> In versions of glibc before 2.22, if size is specified as zero,
>> fmemopen() fails with the error EINVAL. It would be more con‐
>> sistent if this case successfully created a stream that then
>> returned end of file on the first attempt at reading; since
>> version 2.22, the glibc implementation provides that behavior.
>>
>> In versions of glibc before 2.22, specifying append mode ("a"
>> or "a+") for fmemopen() sets the initial buffer position to the
>> first null byte, but (if the file offset is reset to a location
>> other than the end of the stream) does not force subsequent
>> writes to append at the end of the stream. This bug is fixed
>> in glibc 2.22.
>>
>> In versions of glibc before 2.22, if the mode argument to fmem‐
>> open() specifies append ("a" or "a+"), and the size argument
>> does not cover a null byte in buf, then, according to
>> POSIX.1-2008, the initial buffer position should be set to the
>> next byte after the end of the buffer. However, in this case
>> the glibc fmemopen() sets the buffer position to -1. This bug
>> is fixed in glibc 2.22.
>>
>> In versions of glibc before 2.22, when a call to fseek(3) with
>> a whence value of SEEK_END was performed on a stream created by
>> fmemopen(), the offset was subtracted from the end-of-stream
>> position, instead of being added. This bug is fixed in glibc
>> 2.22.
>>
>> The glibc 2.9 addition of "binary" mode for fmemopen() silently
>> changed the ABI: previously, fmemopen() ignored 'b' in mode.
>>
>> EXAMPLE
>> The program below uses fmemopen() to open an input buffer, and
>> open_memstream(3) to open a dynamically sized output buffer.
>> The program scans its input string (taken from the program's
>> first command-line argument) reading integers, and writes the
>> squares of these integers to the output buffer. An example of
>> the output produced by this program is the following:
>>
>> $ ./a.out '1 23 43'
>> size=11; ptr=1 529 1849
>>
>> Program source
>>
>> #define _GNU_SOURCE
>> #include <string.h>
>> #include <stdio.h>
>> #include <stdlib.h>
>>
>> #define handle_error(msg) \
>> do { perror(msg); exit(EXIT_FAILURE); } while (0)
>>
>> int
>> main(int argc, char *argv[])
>> {
>> FILE *out, *in;
>> int v, s;
>> size_t size;
>> char *ptr;
>>
>> if (argc != 2) {
>> fprintf(stderr, "Usage: %s '<num>...'\n", argv[0]);
>> exit(EXIT_FAILURE);
>> }
>>
>> in = fmemopen(argv[1], strlen(argv[1]), "r");
>> if (in == NULL)
>> handle_error("fmemopen");
>>
>> out = open_memstream(&ptr, &size);
>> if (out == NULL)
>> handle_error("open_memstream");
>>
>> for (;;) {
>> s = fscanf(in, "%d", &v);
>> if (s <= 0)
>> break;
>>
>> s = fprintf(out, "%d ", v * v);
>> if (s == -1)
>> handle_error("fprintf");
>> }
>>
>> fclose(in);
>> fclose(out);
>>
>> printf("size=%zu; ptr=%s\n", size, ptr);
>>
>> free(ptr);
>> exit(EXIT_SUCCESS);
>> }
>>
>> SEE ALSO
>> fopen(3), fopencookie(3), open_memstream(3)
>>
>>
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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2016-03-09 4:19 Revised fmemopen(3) man page Michael Kerrisk (man-pages)
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2016-03-11 4:15 ` Adhemerval Zanella
2016-03-11 16:33 ` Michael Kerrisk (man-pages)
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